This invention relates to liquid-containing cans of the type in which a pour hole is covered by a removable pressure-sensitive adhesive tape tab. The invention also relates to end walls useful for the manufacture of such cans and to methods of preparing such end walls.
Over the past several years there has been an increasing use of metal containers for carbonated soft drinks and beer. These containers are opened by lifting and grasping a ring attached to the end wall and removing a portion of the wall along weakened tear lines. Because aluminum is the only commercially available metal which can be formed into a readily openable end wall in this manner, the original "tear-top" cans were made entirely out of aluminum. To make such cans more economical, carbonated beverage manufacturers later resorted to fabricating the tubular side wall and one end wall from steel, using openable aluminum for only the other end wall. In some cases an aluminum insert, including a tear strip was incorporated into a steel can end. Although such dual metal cans are satisfactory for the intended use, it is ecologically desirable today for empty cans to be capable of simple recycling; the separation of the aluminum from steel is both inconvenient and expensive. Additionally, several states and cities have banned the use of ring pull cans because the removed tabs are so commonly dropped on the ground or thrown into a body of water, where they decompose only very slowly.
It is known that unpressurized cans containing tomato juice and similar liquids can be provided with a convenient means for opening by pre-punching a hole in one end wall and applying a pressure-sensitive adhesive tape, tab over the hole. When the user desires to open such a container, he grasps the free end of the tape tab and pulls the closure off, exposing the hole in the end wall to permit pouring out the contents of the can. Easy-open containers of this type are shown in U.S. Pat. No. 3,389,827, the disclosure of which is incorporated herein by reference.
Various attempts have been made to adapt the sealing technology of the aforementioned patent to the packaging of gas-containing liquids such as carbonated soft drinks and beer, but these attempts have not proved commercially satisfactory. Typical pressures for various beverages at 38.degree.C. are as follows: orange pop, 1.7 kg/cm.sup.2 ; strong beer, 3.3 kg/cm.sup.2 ; root beer, ginger ale, cola and lemon, 4.5 kg/cm.sup.2 ; club soda, 5.8 kg/cm.sup.2. At room temperature (21.degree.C.), pressures are about 70% and even under normal refrigeration (e.g., 4-5.degree.C.), they are about 40%, of the values just cited. Such pressures bulge prior art tape closures upward and gradually peel them from the area immediately circumjacent ot the pour hole, and, in a relatively short time, break the seals. Prior to the present time, then, it has been felt that tape closures could not be employed in the sealing of highly pressurized containers.